What to do with the main domain if it only serves as a redirect?

Question

Search Engine Optimization

Hello!
In general, subject. What rules for robots to prescribe so that it does not interfere with subdomains? The main domain serves only to determine the user's language and redirect to the corresponding subdomain: en.site, ru.site, etc . Each subdomain has its own sitemap, etc.

Answer 1

Make a redirect via JS on the user side.
For robots - display the page in English without a redirect on this domain.
In the canonical tag - specify the subdomain for English. language.
And as Evgeny Yudin already said :

Specify "noindex, follow" in the head meta robots.

Answer 2

Specify "noindex, follow" in the head meta robots.
And on subdomains in the hreflang directive, be sure to specify the main domain as the language selection page.